Controlling the output flow of a variable displacement pump is important to maintain a stable hydraulic system. Doing so with accuracy can help protect the system from unintended damage and can aid in improving the overall efficiency of the hydraulic system.
Variable displacement pumps, specifically axial piston pumps, generally include a drive shaft, a cylinder barrel that is rotatable by the drive shaft, multiple piston bores positioned about the cylinder barrel, and multiple pistons positioned within the piston bores and attached to a tiltable swash plate. To control the displacement of the axial piston pump, the angle of the swash plate must be altered. Traditionally changing the angle is accomplished by a swash plate piston cylinder or solenoid. When the swash plate is tilted relative to the longitudinal axis of the drive shaft, the pistons reciprocate within the piston bores to produce a pumping action. Therefore, the larger the swash plate angle, the larger the displacement of the pump.
When controlling the swash plate piston cylinder or solenoid, the pressure from the hydraulic tank and the pressure from the hydraulic circuit are typically considered. For example, if a hydraulic spring-loaded piston cylinder is used to control the angle of the swash plate, tank pressure can act on one side of the piston and hydraulic circuit pressure can act on the other side of the piston. Depending on the difference between the two pressures and the spring constant, the piston will move within the cylinder accordingly. Because the piston is also attached to the swash plate, as the pressure difference changes and moves the piston, the swash plate angle also changes, thereby changing the displacement of the pump.
In other examples, when the swash plate is controlled by the action of a solenoid, the change in displacement of the pump is commonly proportional to the current supplied to the solenoid by a controller.
Customized real time control of the displacement of the pump is often desired. Therefore, the piston cylinders or solenoids often are configured to allow for the on-demand altering of the pump displacement. Additionally, hydraulic pressure within the hydraulic circuit can change abruptly during operation. Such changes can be caused by a failure, excess load, etc. Additionally, electronics controlling the displacement of the pump (i.e., by solenoid) can also fail, causing a drastic increase in pressure. Therefore, a separate pressure compensator device is often included as part of the system to safeguard the system in such scenarios.
Improvements in variable displacement pump control are desired.